The market for superconductor products has been growing, especially in light of a significant expanding commercial application. More specifically, high temperature superconductor (“HTS”) devices and systems have been successfully employed in cellular communication base station filters. Such filters are designed to reduce signal interference and increase base station sensitivity.
To operate in their intended manner, superconductor devices must generally be cooled to extremely low temperatures. For current HTS devices, the devices must be cooled to about seventy-seven (77) K or lower. These cryogenic temperatures can be reached using a cryocooler or by submersing the device to be cooled in a fluid which boils at a low temperature. Liquids that are commonly used to achieve cryogenic temperature are Nitrogen, which boils at seventy-seven (77) K and Helium, which boils at four (4) K. Cryocoolers generally operate by either controlled evaporation of volatile liquids (using the heat of vaporization as the means to cool), by controlled expansion of gasses confined initially at high pressure (such as 150 to 200 atmospheres), or by acting as a heat-pump by alternatively expanding a gas near the area to be cooled (absorbing heat by the so-called heat of expansion), then compressing the gas at another location (removing the heat by the heat of compression) in a closed-cycle. One of the highest efficiency cryocoolers is a closed-cycle cryocooler based upon the Stirling cycle.
Stirling cycle refrigeration units (or Stirling cycle cryocoolers) typically comprise a displacer assembly and a compressor assembly, wherein the two assemblies are in fluid communication with one another. The assemblies are generally driven by a prime mover. The prime mover may be implemented with an electromagnetic linear or rotary motor.
Conventional displacer assemblies generally have a “cold” end and a “hot” end. The hot end is in fluid communication with the compressor assembly. Displacer assemblies generally include a displacer having a regenerator mounted therein for displacing a fluid, such as Helium, from one end (i.e., the cold end) of the displacer assembly to the other end (i.e., the hot end) of the displacer assembly. The compressor assembly functions to apply additional pressure to the fluid when the fluid is located substantially within the hot end of the displacer assembly, and to relieve pressure from the fluid, when the fluid is located substantially within the cold end of the displacer assembly. In this fashion, the cold end of the displacer assembly may be maintained, for example, at seventy seven (77) K, while the hot end of the displacer assembly is maintained, for example, at fifteen (15) degrees above ambient temperature (e.g., at about 313 K).
One of the drawbacks of current cryocoolers is the use of a large number of components. In particular, there are a number of components that make up the external housing. Since the device operates by compressing and expanding a fluid, the cryocooler must be completely sealed. In practice, the various components are brazed together in order to accomplish this requirement (e.g., to seal the cryocooler from ambient atmosphere). However, brazing is very labor intensive. Further, the brazing operation often introduces unwanted variances in the linearity of the assemblies. This increases the required tolerances in the device and has lead to including additional component parts to accommodate the larger required tolerances and non-linearities.
Another drawback of current cryocoolers is the inclusion of various components into the interior of the cryocooler. Many of these components exhibit outgassing (e.g., the diffusion of gas from the component into the internal sealed environment of the cryocooler). Examples of components that may outgas include the motor coil, the outer lamination, and epoxies used to bond various components together. By introducing unwanted gasses into the internal sealed environment, gassing often lowers the efficiency of the cryocooler.
Accordingly, there is a need in the art to develop a cryocooler with a minimum of components forming the external sealed housing. By doing so, the concentricity alignment between components may be improved. Further, there is a need for design flexibility of the external sealed housing related to utilizing both inner and outer motors. The present invention directly addresses and overcomes the shortcomings of the prior art.